I was kind of confused while I was reading about this. Is this actually something that people would use when wanting to become a vampire or is it just a myth? Is it something more than a prayer? Does it really work?
I'm guessing that a lot of the confusion comes from the fact that it is not technically a "spell", but a poem. There is a tradition among vampire worshipers of writing poems to Selene as the first vampire did while he was still human.
So the question then is - how does a poem written to Selene help me become a vampire? Well, let me begin by saying that there is no magic spell that can make you into a vampire, and since vampires are living in the corporeal (physical) world, they cannot be summoned like spirits and demons. Therefore the only way to become a vampire is to get bitten or otherwise infected by the bacteria in their blood.
I don't have any proof that Selene's Prayer will actually summon a vampire to anyone who reads the prayer aloud with the intention of calling a vampire to them, but if you look at the words, it seems that this is exactly what this poem is for. Since this is the only type of poem/spell/chant/prayer that seems to be specifically for this purpose, I have to think that this represents a person's best chance to attract a vampire to themselves. Since there is not 1-800 number you can call to request a vampire, I'd say that reciting this prayer is better than nothing.
Does it work? I don't know, I haven't tried it. Not because I think it doesn't work, but because I don't want to attract vampires to myself. I don't see any reason NOT to recite it, though. Best case scenario (assuming you want to become a vampire) is that reciting it nightly with deep intention of an outcome will eventually attract a vampire. Otherwise, it is a minor time investment and you can leave it at that.
If anyone has any experience with this prayer, feel free to comment here.